.

Attached strain gauges to top and bottom of a new aluminum tab and connected them into a half Wheatstone bridge circuit.

Secured one end of the tab and applied 10 lbs of force to the opposite end end. Measured the output voltage differential from the bridge circuit.

Designed the corresponding instrumentation amplifier circuit based on the observed output voltage sensitivity.

Removed the old tabs from the pushrim and welded the three new tabs onto the pushrim.

Constructed the Wheatstone bridge and instrumentation amplifier circuit for each of the three pushrim tabs on a printed circuit board.

Wired the wheel, attached the strain gauges to the tabs, connected the strain gauges to the Wheatstone bridge, and mounted the printed circuit board to the spokes of the wheel.

Tests revealed output voltage response to applied resultant force. An empirical best fit model was constructed to relate resultant force to output voltage.

Manual wheelchair users (MWUs) are living longer and fuller lives due to innovative technological and medical advances. While the progress has been substantial, there are still areas of need in this population. More than half of MWUs experience upper extremity (UE) pain and injury 1,2,3. The UEs serve as the principle means for mobility, therefore, any impeding factor, such as pain or injury, can lead to a decreased quality of life. The development of UE pain and injury may be a result of improper propulsion biomechanics or poor wheelchair seating configurations. In order to quantitatively assess a MWU's propulsion technique for training or seating purposes, there is a need for an instrumented assessment tool. .

INTRODUCTIONINTRODUCTION

Instrumented Wheel for Wheelchair Propulsion AssessmentJacob Connelly, Andrew Cramer, John Labiak, Paul King, Ph D., Mark Richter, Ph.D.

Vanderbilt University Department of Biomedical Engineering, Nashville, TN, USAMax Mobility LLC, Nashville, TN, USA

GOALS & OBJECTIVESGOALS & OBJECTIVES

Develop an instrumented wheelchair wheel utilizing strain gauges.

Quantitatively measure resultant force during wheelchair propulsion.

Minimize costs in order to provide an affordable tool for wheelchair seating clinics.

o Production cost less than $2,000o Market price $3,000 to $5,000

Integrate universal compatibility into the design of the instrumented wheel.oCapable of fitting all wheelchairs.oAdaptable to different size wheels (24'', 25'', and 26'').oProvide wireless capability with Bluetooth technology.

AcknowledgmentsAcknowledgments

METHODSMETHODS

RESULTS AND DISCUSSION RESULTS AND DISCUSSION

At its completion, Prototype I was tested in LabVIEW. Due to the low CMRR and lack in amplification, changes in the output voltage – regardless of the forces applied to the pushrim – were immeasurable. Steps taken to increase CMRR included the addition of a low-pass filter. No significant differences were observed. Thus, Design began on Prototype II.

CONCLUSION

Russel Rodriguez M.E. – Project Engineer, Max Mobility LLCAdam Karpinsky M.E. – Project Engineer, Max Mobility LLCGuo Liyon M.E. – Project Engineer, Max Mobility LLCFranz Baudenbacher, Ph D.– Consultant, VUSE BMETobias Meyer – Consultant, VUSE BME

•Attachment of strain gauges to the top and bottom of the tabs that connect the pushrim to the wheel.

Strain gauges were configured into a voltage divider circuit with a 4.5 V power source.oOutput voltage sent into an 8-pin DAQ unit with Bluetooth wireless transceiver.

The output data was processed in LabView. Low CMRR and absence of aplification yielded immeasurable results.

Implemented a low pass filter for testing in attempt to reduce noise unsuccessfully.

Designed new pushrim tabs in SolidWorks: reduced thickness (0.125'' 0.09'') and width (0.50'' 0.40'') to make pushrim less rigid.

1 Sie IH, Waters RL, Adkins RH, Gellman H. Upper extremity pain in the postrehabilitation spinal cord injured patient. Arch Phys Med Rehabil. 1992;73:44–

48.2 Dalyan M, Cardenas DD, Gerard B. Upper extremity pain after spinal cord injury. Spinal Cord. 1999;37:191–95. 3 Gellman H, Sie IH, Waters RL. Late complications of the weight-bearing upper extremity in the paraplegic patient. Clin Orthop. 1988;233:132–35.

ReferencesReferences

PROTOTYPE I

PROTOTYPE II

T

C

Design Element

Prototype 1 Prototype 2 Description

Pushrim Attachments

Decreased the number of push-rim attachments from 6 to 3 in order to decrease rigidity of push-rim.

Tab Design Changed tab dimensions in order to increase sensitivity through increased flexibility.

Circuit Design

Redesigned circuit to increase CMRR and amplify the voltage output signal.

Completed Wheel

The completed wheel design functions to produce resultant force as a function of voltage.

Placeholder

Placeholder

PROTOTYPE I

PROTOTYPE II

STANDARD CURVE

RESULTANT FORCE

Placeholder

Placeholder

Placeholder

Graphical Analysis (Image)

Graphical Analysis (Image)